Shelby Daytona upgraded to 800 - It is expensive, but good in multiplayer races I find.
But my favourite is the Nissan GTR-R34, great handling and acceleration and looks amazing.
I use A class all the time for both Rivals and Online road trips: the classics (Alfa 33 Stradale, Shelby Daytona, etc) are probably the best of them all but they are predictable & I find too many people driving them nowadays. If you want something slightly different, I recommend:
Lotus Exige S (very balanced, can handle all conditions)
Subaru 05’ WRX (Mine is set up for Time Attack but there are loads of options for this car)
BMW M3 E92 (Built it for fun initially but it suprised me how fast it is when driven well)